1. Field of the Invention
The present invention relates to bolts for rock strata reinforcement and, more particularly, to sheathed cable bolts that are anchored prior to tensioning, tensioned, and post-grouted with a cementitious material.
2. Description of Related Art
Roof and wall support in mining and tunneling operations reinforce rock strata in the roof and walls to prevent the possibility of a collapse. Rock bolts, including solid rigid shaft bolts and flexible cable bolts, are commonly used to consolidate the rock strata. In one form, a rock bolt is point anchored in the blind end of a bore hole, tensioned, and then grouted. The rock bolt may be point anchored by locating a resin cartridge in the blind end of the bore and rotating the rock bolt to burst the resin cartridge and mix its contents. The rock bolt may also be point anchored using a mechanical anchor, such as an expansion shell, that expands in the bore to anchor the bolt. Once anchored, the bolt is tensioned and a cementitious grout is inserted into the bore. The rock bolt may also be provided with a sheath or sleeve, which in combination with the post-grouting, provides corrosion protection for the bolt when used in corrosive environments.
U.S. Pat. No. 5,636,945 to Nes discloses a rock bolt having a tube extending over the bolt to form an annular passage. A nut is threaded on the outer end of the bolt and engages a spherical support. An opening of the support is threaded to engage the external threads on the tube. The bolt is anchored by tightening the nut to expand an expansion bushing.
U.S. Pat. No. 4,850,746 to Finsterwalder et al. discloses a rock anchor having an elongated anchor rod laterally enclosed by an axially elongated sheathing tube with slight play so that the tension member can extend independently of the sheathing tube. An anchor nut is threaded onto the trailing end of the rod to engage a flange of the sheathing tube positioned adjacent a dish-shaped anchor plate.
U.S. Pat. No. 7,381,013 to Rataj et al. discloses a rock bolt having threaded second end with a nut threadably secured thereon. A sleeve surrounds a portion of the bolt to form an annular passage between the sleeve and the bolt. The nut is disposed within the interior of a cup that extends into a bore hole. An annular flange of the cup is attached to a second end of the sleeve. A first end of the sleeve is provided with a cap that engages the bolt.
U.S. Pat. No. 5,525,013 to Seegmiller et al. discloses a cable bolt having a sleeve element crimped to an upper end of the bolt, a “birdcage” enlarged section, and an epoxy-flow dam element. The dam element includes a split ring having a shoulder with a T-extension that engages a T-slot. In a further embodiment, a cable bolt includes a tubular member surrounding the bolt and secured to the bolt via receiving jaws.
U.S. Pat. No. 7,037,046 to Fergusson discloses a cable bolt having a threaded end fitting at a near end of the bolt that cooperates with a load plate, grout injector, and nut. In a particular embodiment, a plastic tube is disposed over a portion of the bolt for the installation of grout and the far end of the cable bolt includes an expansion anchor to enable installation of the bolt.